1. Field of the Invention
The present invention relates to an uninterruptible power supply module. More specifically, the present invention relates to an uninterruptible power supply module having an auxiliary switch element.
2. Descriptions of the Related Art
With advancement of power supply technologies, uninterruptible power supply modules have emerged as an indispensable part of a power supply system. An uninterruptible power supply module operates in the following way. When alternating-current (AC) voltage source operates normally, the uninterruptible power supply module receives power from AC voltage source, and regulates the AC voltage to a regulated AC output voltage to load. On the other hand, in case AC power source failure or an abnormal voltage exceeding a predetermined value occurs, the uninterruptible power supply module will operate to switch the circuit to a direct-current (DC) voltage source (e.g., a battery) by a power source selection switch (e.g. a relay), so that a DC voltage supplied by the DC voltage source is modulated by the UPS, and the UPS supplies an AC voltage to power the load. By means of the power supply switching, a continuous power supply is maintained for the load. Unfortunately, conventional uninterruptible power supply modules are usually both oversized and overweight.
To solve these problems, U.S. Pat. No. 6,104,104 discloses an uninterruptible power supply module adopting a new control method, in which an electrolytic capacitor conventionally used for an uninterruptible power supply module is replaced by a small capacitor. This results in significant reduction in both volume and weight of the capacitor and enhances reliability of the uninterruptible power supply module as a whole.
However, the power source selection switch in such an uninterruptible power supply module is a mechanical switch with a relatively long switch time (millisecond level). Before completion of the switching from the primary AC power source to the battery, the small capacitor described in U.S. Pat. No. 6,104,104 is unable to supply adequate energy to the load during the switch process. Consequently, a temporary interruption inevitably exists in the output voltage during the switch process, which greatly endangers reliable operation of the load. Moreover, when the mechanical switch operating, a large current may cause failure of the switch process, or even cause arcing between associated contacts and consequent burnout of the mechanical switch.
In view of this, efforts still have to be made in the art to provide an uninterruptible power supply module that can ensure a safe and reliable switch process, thereby to continuously supply a constant current to a load.